/Engine/Plugins/Experimental/RenderGrid/Source/RenderGrid/Public/RenderGrid/RenderGrid.h
In here, you could do any cleanup required at the end of rendering out a job, like for example undoing the changes you've made to the world for this job.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintImplementableEvent, Meta=(DisplayName="EndViewportRender")) void ReceiveEndViewportRender ( [URenderGridJob](API\Plugins\RenderGrid\RenderGrid\URenderGridJob) * Job )